Don't curse the cold: Shivering may help burn body fat

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If you're looking for a silver lining in the winter cold-fest, look no further than your waistline. Shivering may be as good as exercise to help you drop a few pounds, a study found.

Shivering's weight-loss upside is linked to a hormone produced by the body's muscles, according to research from the National Institutes of Health published in the journal Cell Metabolism. When a body trembles from the cold it releases irisin, also known as the "exercise hormone," which stimulates fat tissue to produce heat so the body can maintain its core temperature.

Irisin was first discovered two years ago and is a kind of messenger hormone relaying beneficial information to body tissues. Increases in irisin turns the body's white fat into the more metabolically active brown fat, which helps the body burn more calories. It also may make the body more sensitive to glucose.

The researchers wanted to find out if shivering could produce the same effects on irisin as exercise, explains lead author Dr. Francesco S. Celi, chair of the division of endocrinology and metabolism at Virginia Commonwealth University, who has been studying "adaptive thermogenesis," basically how our bodies react to temperature changes. "From an evolutionary perspective, shivering is the last resort to maintain core temperature."

Ten healthy volunteers of normal weight and good health participated in three different experiments designed to measure irisin levels. First, participants exercised at maximal aerobic capacity on a stationary bike. Researchers then measured their energy expenditures. Blood samples were also taken. To induce shivering, participants were put under cooling blankets set to slightly more than 53 degrees Fahrenheit. The researchers found that irisin levels produced through exercise were comparable to shivering.

To help confirm their results, the researchers tested the effects of irisin on cultures of adipose, or fat, tissue cultures. They found that irisin did help stimulate production of specific proteins linked to brown fat, essentially making the white fat cultures more similar to that of the more metabolically active brown fat.

Although the researchers are not saying we should dump our parkas for T-shirts when it's 12 degrees outside, they do think there is something to be said for finding ways to burn more energy.

"The general equation is weight gain is a sustained imbalance between energy intake and expenditure, and we live in an environment that is completely artificial, a perennial spring," says Celi, who was with the NIH when the research was performed.

"That's all designed to decrease the amount of energy we need to expend and that can lead to health problems," particularly diabetes and other metabolic issues such as lipid profiles.

The hope is that these findings, and others, will eventually lead to some type of pharmacologic intervention to promote irisin production, and perhaps stem the tide of obesity.

"Exercise is important, but so is weight loss, and people often overestimate how much exercise they are doing and wind up eating more," says Celi. "There are not many people who can lose weight just through exercise, but if we could find a way to increase brown tissue (fat), we could help very many people get healthy."

In the interim, we could stand outside for a few seconds or do what a scientist does. While Celi doesn't copy one of his colleagues who "only cold showers now," he says, "I did lower the thermostat a bit at home."